One or more cylinders of an engine may be temporarily deactivated to improve vehicle fuel economy. The one or more cylinders may be deactivated by ceasing to supply fuel and spark to the deactivated cylinders. Additionally, air flow into and out of the deactivated cylinders may be prevented, or at least significantly reduced, via closing intake and exhaust valves of the deactivated cylinders. Air or exhaust gases may be trapped in the deactivated cylinders to maintain higher pressures in the deactivated cylinders and to recycle energy put into compressing gases in the cylinders.
The engine's crankshaft and firing order are defined to reduce engine noise and vibration when the engine is operating with all its cylinders in an active state. Engine torque production and engine speed may be smoothest (e.g., producing least variation from desired engine torque and desired engine speed) when the engine is operated with its full complement of cylinders. If one or more engine cylinders are deactivated, engine torque variation and engine speed variation from desired values may increase because of longer intervals between combustion events. As such, engine fuel economy may be increased via deactivating cylinders, but noise and vibration from the engine as observed by vehicle occupants may increase. If the engine is operated with higher levels of noise and vibration, vehicle occupants may find riding in the vehicle objectionable. Thus, it may be difficult to provide higher levels of fuel efficiency without degrading the driving experience.
The inventors herein have recognized the above-mentioned limitations and have developed an engine control method, comprising: increasing an actual total number of available cylinder modes from a first actual total number of available cylinder modes to a second actual total number of available cylinder modes via a controller in response to an estimate of roughness of a road exceeding a threshold; and operating an engine via the controller in a cylinder deactivation mode after increasing the actual total number of available cylinder modes.
By increasing the actual total number of available cylinder modes in response to an estimate of roughness of a road exceeding a threshold, it may be possible to provide the technical result of operating an engine in a cylinder deactivation mode at a time when vehicle occupants may be less likely to notice the additional engine noise and vibration. For example, if a vehicle travels down a rough road, the actual total number of available cylinder modes may be increased to allow the engine to operate with two or more deactivated cylinders, whereas if the vehicle operated on a smooth road but otherwise similar conditions, cylinder deactivation for the engine may be prohibited based on engine speed and engine torque.
The present description may provide several advantages. In particular, the approach may provide improved vehicle fuel economy. In addition, the approach may reduce the possibility of disturbing occupants of a vehicle while cylinders are deactivated. Further, the approach may enable or deactivate cylinder deactivation modes responsive to sprung and unsprung vehicle mass so that fuel economy may be increased while vehicle occupants may be less susceptible to noise and vibration that may be related to deactivating engine cylinders.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.